RE-Fe-B type magnet alloys have recently been developed as materials for permanent magnets with comparatively low cost and with significantly high magnetic properties. Isotropic magnets of this type can be made into various types of anisotropic magnets, i.e., axial, radial and planar anisotropic magnets, by hot plastic working which induces crystallographic alignment. In the production of these magnets, several techniques are employed: (a) rapidly solidifying RE-Fe-B type alloy melt to obtain amorphous or fine crystalline powder followed by hot compacting/pressing and plastic deforming, (b) hot plastic deforming of suitable cast alloys, and other appropriate methods.
However, because of relatively poor hot workability of some RE-Fe-B alloys, cracks were generated during hot working of the alloys. This is the reason why higher degrees of deformation have not been utilized in actual production practices although it would be expected that higher magnetic properties could be obtained at higher degrees of deformation. When such high levels of deformation were applied, cracking was so severe that sound products could not be obtained in some cases.
In addition, hot working is usually conducted at temperatures not lower than about 750.degree. C. to 800.degree. C. so as to induce sufficient anisotropy and hence higher remanence. At such high temperatures, fine crystalline grains obtained by rapid quenching grow coarse, which results in a decrease of intrinsic coercivity. Shorter die life has also been a problem at such temperatures.
Some applicants of the present application previously proposed a method of working which was characterized by the application of appropriate hydrostatic pressure on a free surface of the material in order to cope with the above-mentioned problems during backward extrusion for manufacturing radially oriented magnets (Japanese patent application no. TOKUGAN HEI 1-293873). However, a complicated apparatus is necessary to practice the proposed method, and this leads to higher production costs. Furthermore, in inducing axial magnetic anisotropy by upsetting, it is difficult to avoid the generation and growth of cracks by such method.
An object of the present invention is, therefore, to provide various compositions of rare earth magnet alloys endowed with excellent hot workability. Such improved workability is seen in a marked reduction in the tendency of the material to crack during hot working and in a reduction in the required hot working temperature. The present inventors have processed and evaluated various rare earth magnet alloys in order to improve the hot workability of these alloys. Alloys with certain compositions have been found to have much improved hot workability.